Megilat Esther is considered holy writ; therefore, it must be written in the way a Torah scroll is written, in black ink on parchment. If it is written using something other than ink, or on paper, it is invalid, and one who reads from it has not fulfilled his obligation. The hide from which the parchment is made must be tanned for the sake of writing a Megilla. The individual sheets of parchment must be sewn together with threads made of sinews. One must etch out the lines using a stylus before commencing to write on the parchment, so that the words come out straight. Furthermore, it must be written by hand, and the scribe must be mindful of the sanctity of the Megilla.
When writing a Torah scroll, we make sure that all of its letters are written according to their exact configurations, that no letters touch each other, and, of course, that no letters are omitted or added unnecessarily. A scribe should likewise be careful about all these things when writing a Megilla. Be-di’avad, however, there is a difference between a Torah scroll and Megilat Esther: one may not recite the berakha over reading the Torah if the scroll contains a mistake in even one letter, but one may read from, and recite a berakha over, a Megilla that is missing some of its letters, if a perfectly kosher scroll is unavailable. For example, if a scribe mistakenly omitted several letters from a Megilla, or wrote them incorrectly – or if he originally wrote the scroll properly, but some of its letters faded over time – one may still use it to perform the mitzva, as long as the main part of it is written properly. The reason for this is that the Megilla is called a “letter,” indicating that its purpose is to tell the story from a written document, but it does not need to be as precise as a Torah scroll must be. We learn from here that one fulfills his obligation as long as the essentials of the Megilla are written properly, and on condition that one fills in the missing words by reading them from a printed Megilla or by reciting them by heart.
Technically, one may write a translation of the Megilla, with ink on parchment, for someone who does not understand Hebrew, and by reading this translation, he can fulfill his obligation to read the Megilla. For example, one who knows only English may acquire an English translation of the Megilla, written in ink on parchment, and read from it (sa 690:8-11). We do not follow this ruling in practice, however, since we do not know how to translate the words precisely. Rather, one fulfills his obligation by hearing the Megilla in Hebrew even if he does not understand it, as long as he has the intention to fulfill the mitzva of Megilla reading (sa 690:8, mb ad loc. 32, ahs ad loc. 15).
. The rule is that one fulfills his obligation, be-di’avad, if he reads from a Megilla of which at least half is written properly, provided that no part of the story is entirely missing and that the beginning and end are intact (sa 690:3).
Some maintain that if some of the words are written in a different language, the Megilla is invalid, because it is like a document that is self-evidently counterfeit. Mateh Yehuda and R. Shlomo Kluger maintain that a Megilla is disqualified from use if letters are missing or added in a way that changes the meaning of a verse, because it, too, is like a self-evidently counterfeit document. In practice, though, most authorities maintain that mistakes do not invalidate a Megilla any more than erased letters do, as explained in mb 691:6, 14. See also bhl 690:8, regarding the alternative opinion, and Ritva.
One should not write vowels, cantillation marks, or berakhot in the Megilla, but be-di’avad, when no other scroll is available, one may read from such a Megilla and even recite a berakha over it (sa 691:9). A Torah scroll, however, is invalidated if vowels and cantillation marks are written inside (sa, yd 274:7). There is a stringency regarding the public reading of the Megilla: If one reads from a Megilla that is written together with other books of the Writings (Ketuvim), one does not fulfill his obligation. This is because the miracle is not publicized this way, as it looks like one is merely reading from the Writings. An individual, however, discharges his obligation when reading from such a Megilla (sa 691:8).
Some rule very leniently and allow one to read from an invalid Megilla (like the ones children use, which open like a scroll) with a berakha, if no kosher Megilla is available (Roke’aĥ, Orĥot Ĥayim). According to most poskim, however, under no condition may one recite a berakha on such a Megilla. Nonetheless, it is proper to read from it without a berakha (sa 691:10). mb ad loc. 26 adds that even if the only Megilla one has is a printed book, he should still read from it, so as to remember the story.